Hepatitis B virus (HBV) is the most prevalent human tumor virus. It is estimated that chronic HBV infection causes 1,000,000 cases of liver cancer annually. HBV must actively replicate within liver cells to maintain its chronic infection. We work to understand how HBV carries out the individual steps by which it replicates its genome in order to understand how this virus contributes to human cancer. To date, most insights into hepadnavirus DNA replication have come through the study of the avian hepadnavirus, duck hepatitis B virus (DHBV). Over the past decade, our laboratory has made multiple contributions to the understanding of hepadnavirus DNA replication through the study of DHBV. A general theme has emerged from our studies recently: the dynamic conformation of the viral genomic nucleic acid makes multiple contributions to its own replication. Our analyses have elucidated two fundamental mechanisms that contribute to the template switching during avian hepadnavirus plus-strand synthesis: 1) a small DNA hairpin suppresses in situ priming, and therefore contributes to primer translocation; and 2) base pairing between the three cis-acting sequences 3E, M, and 5E contributes to both plus-strand template switches, presumably by juxtaposing the donor and acceptor templates for primer translocation and circularization. In addition, we discovered the mechanism by which DHBV supports the simultaneous accumulation of unspliced and spliced RNA. An RNA secondary structure that contains the 5' and 3' splice sites suppresses splicing to permit the accumulation of pgRNA. This proposal has three aims: 1) to understand the mechanism of the template switch after the synthesis of the fourth nucleotide of minus-strand DNA; 2) to determine whether the viral P protein makes specific contributions to plus-strand template switching; and 3) to understand the role of the spliced RNA in the life cycle of DHBV. [unreadable] [unreadable] [unreadable]